Introduction: Lateral interbody cages have proven useful in lumbar fusion surgery. Spanning both lateral cortical rims while sparing the Anterior Longitudinal Ligament they restore disc height, improve coronal balance and add stability. The standard approach to their insertion is 90 degrees lateral transpsoas which is bloodless compared to other techniques of interbody cage insertion but requires Neuromonitoring and at L4/5 can be difficult because of iliac crest obstruction or an anterior plexus position. . The oblique muscle splitting approach with the patient in a lateral position, remains retroperitoneal, and on the left side enters the disc space through a window between psoas and the common iliac vein. Reports of this approach are few and none previously have described how to use large lateral type cages so effective at restoring spinal alignment

Methods: Prospectively gathered retrospectively analysed data on initial 20 consecutive patients who underwent anterior to psoas (ATP) fusion for degenerative conditions including L4/5. Data collected included serial ODI., VAS and evidence of postoperative and complications

Results: Improvements in both ODI and VAS scores produced clinical outcomes comparable with transpsoas approach. Approach related complications included transient thigh weakness in five (5) patients and transient dysesthesias in the anterior and medial thigh in eight (8) patients were seen in the first half of the series but changes to retractors and technique to ensure stable psoas retraction reduced complications. There were no vascular injuries or other serious events.

Conclusions: The anterior to psoas corridor provides simplified access for large lateral cages in lumbar fusion surgery compared to transpsoas approach. Approach related complications in the first 20 patients were comparable to transpsoas approaches.

Patient Care: It will possible open a way to minimize morbidity related to lumbar plexus injuries common in the transpsoas approach

Learning Objectives: By the conclusion of this session participants should be able to: 1) discuss in small groups of importance of safety in lateral approach surgery 2) complications and their causes and avoidances #) anterior to psoas surgical corridor

References: 1) Elowitz EH, Yanni DS, Chwajol M, Starke RM, Perin NI. Evaluation of indirect decompression of the lumbar spinal canal following minimally invasive lateral transpsoas interbody fusion: radiographic and outcome analysis. Minim Invasive Neurosurg 54(5-6):201-6, 2011. 2)Moller DJ, Slimack NP, Acosta FL, Koski TR, Fessler RG, Liu JC. Minimally invasive lateral lumbar interbody fusion and transpsoas approach-related morbidity. Neurosurg Focus 31(4):E4, 2011. 3) erjano P, Lamartina C. Minimally invasive lateral transpsoas approach with advanced neurophysiologic monitoring for lumbar interbody fusion. Eur Spine J 20:1584-1586, 2011.